B-lymphocyte antigen CD19 also known as CD19 (Cluster of Differentiation 19), is a 95 kDa type-I transmembrane glycoprotein which is restricted to B cell antigen. On the B cell surface, CD19 associates with CD21, CD81 and Leu-13 to exert its function. CD19 is also found on the follicular dendritic cells and the early cells of myelomonocytic lineage but not on normal T cells, NK cells, monocytes, granulocytes, erythrocytes and platelets.